5 2 



THE ANATOMY OF WOODY PLANTS 



distribution of parenchyma tous elements. In a is shown the trans- 

 verse view, and it is here clear that the cells in question, accentuated 

 by the representation of their walls in black, are confined to a posi- 

 tion at the end of the annual ring. Clearly, the vessels appearing 

 in the figure are unaccompanied by any parenchymatous elements. 

 In b is represented the longitudinal radial aspects of the same wood, 

 and it becomes clear that in this plane, too, the storage cells are 

 confined to the terminal region of the annual ring, for none can be 

 seen in relation to the vessels. The situation here indicated is not 



FIG. 39. Terminal parenchyma in Popidus. Explanation in the text 



uncommon in the case of woods with reduced vasicentric paren- 

 chyma. As in so many other instances, the situation is made clear 

 by reference to more conservative parts, such as the root and the 

 first annual ring of the stem, or to injured material showing a 

 reversion to the primitive condition. By such control of evidence 

 it becomes clear that in the Salicaceae, as well as in Magnolia and 

 Liriodendron among the Magnoliaceae, the characteristic mode of 

 distribution of the storage cells is vasicentric, for they occur in this 

 manner both in conservative organs and parts and likewise as the 

 result of experimental injury. It cannot, of course, be too strongly 

 emphasized in the case of comparative anatomical investigations 

 that a wide view of any particular situation is essential to an ade- 



